Cleansing compositions which are immersed in the flush water cistern of a lavatory bowl or urinal and are slowly dissolved to release an active ingredient which serves to assist in cleansing the lavatory bowl or urinal when water is flushed from the cistern into the lavatory bowl or urinal are well known. Such products are generally of two types, the dispenser type and the drop-in type. The dispenser type employs a container or a two-component metering device containing two incompatible cleansing compositions but is an inconvenient and messy component of the product which must be removed from the tank and disposed of when the chemicals are exhausted. The drop-in type product eliminates this problem but reintroduces all of the problems which the dispenser was designed to circumvent.
It has long been known that both iron and manganese cause serious staining problems in potable and industrial water systems. The most common form in which these elements are found in the water systems are as soluble ferrous carbonate and manganeous bicarbonate. Household water generally contains about 0.05 mg/l of manganese and of about 0.3 mg/l of iron, usually in the form of soluble salts. When the concentration of oxidizing agents in the household water, such as residual chlorine, is higher than 0.5 mg/l, the manganese and iron are slowly oxidized, especially at pHs above 7, on the porcelain surfaces and form water insoluble manganic or ferric compounds, respectively. These precipitates adhere to the porcelain surface and eventually form a dark brown stain, especially the water-porcelain-air interface where water evaporation takes place resulting in what is commonly called "toilet bowl ring". The ring may also contain other mineral deposits such as calcium and magnesium carbonates and sulphates and organic matter.
There have been previous attempts to inhibit the formation of the mineral stain on the porcelain surface of the water closets and some of these are described in U.S. Pat. Nos. 4.283,300, 4,302,350, 4,428,872 and 4,452,713. These patents describe the use of water soluble polymers or copolymers, such as partially hydrolyzed polyacrylamides, salts of polyacrylic acid, copolymers of ethylene and maleic anhydride and copolymers of methyl vinyl ether and maleic anhydride. These polymers and copolymers contain multiple carboxylate or carboxylic acid moieties which provide them with the properties of a chelating agent, permitting the polymers to sequester metal ions such as iron and manganese. The patents describe a method for cleaning the domestic water closet by dispensing the polymeric chelating agent and an oxidizing agent separately in a two-compartment system which is capable of dispensing the ingredients into the water closet concurrently and independently. However, as previously noted, the two-compartment dispenser system is very difficult to practice in addition to being costly.
Another approach is to make surfactant cleansing blocks by tabulating, casting or extrusion. This is described for instance in U.S. Pat. Nos. 4,043,931, 4,269,723, 4,460,490, 4,438,015, 4,722,802, 4,738,728 and 4,082,449. The surfactant in these cleansing blocks is released gradually over an extended period of time to clean the porcelain surface of the water closets. None of these, however, attempt to inhibit the initial formation of the mineral stain on the porcelain surface.
It is accordingly the object of this invention to provide a cleansing block, for use either as a drop-in type or a dispenser type employed in a container, which operates to inhibit the formation of a mineral stain on the porcelain surfaces of a water closet. This and other objects of the invention will become apparent to those of ordinary skill in this art from the following detailed description.